In an automotive vehicle, there is a known method of using a sensor for spectrometric analysis of the vehicle's fuel. Thus, sensors for spectrometric analysis of liquid fuel such as gasoline or diesel fuel, for example, and sensors for spectrometric analysis of pressurized variable-pressure gaseous fuel such as methane or dihydrogen for example, are known.
Such sensors are fitted in the fuel routing circuit linking the fuel tank to the engine, and comprise, in a known way, a tube through which the fuel flows. This tube comprises two transparent or translucent portions, called windows, positioned facing one another so as to allow the passage of an optical flow through the fuel flowing in the tube.
Having passed through the tube, and consequently through the fuel flowing in the tube, the optical flow is received by a receiver, which performs a spectrometric analysis on it in a known way to determine the composition of the fuel. This analysis of the fuel composition may be used by an electronic control unit of the vehicle, for example in order to optimize the injection of the fuel into the engine.
In a sensor for spectrometric analysis of a variable-pressure gaseous fuel, the distance between the two windows for the passage of the optical flow, called the optical path, depends on the pressure of the gas to be measured. Thus, for example, the value of the optical path must be large for low-pressure gases, for example 10 mm, whereas the value of the optical path for high-pressure gases must be small, for example 2 mm.
Thus, if the optical path is not adapted to the gas pressure, the signal generated by the sensor may be noisy, that is to say imprecise. This may result in an incorrect spectrometric analysis, which is a major problem. Consequently, if the gas pressure varies over time, the optical path is not necessarily adapted to the different pressure values of the gas flowing in the sensor.